Capsular polysaccharides are important immunogens found on the surface of bacteria involved in various bacterial diseases. This feature has led to them being an important component in the design of vaccines. They have proved useful in eliciting immune responses especially when linked to carrier proteins (Ref. [1]).
Reference [2] describes a method for preparing capsular polysaccharides, particularly from Streptococcus agalactiae (also referred to as Lancefield's Group B Streptococcus, or GBS). The method comprises: (a) providing a crude isolate containing the capsular polysaccharide; (b) removing an alcohol precipitate formed by contacting the crude isolate with an alcohol solution; (c) ultrafiltration using a cellulose membrane having a cut-off of about 30 kDa to remove smaller molecular weight components while retaining the capsular polysaccharide; (d) removing protein contaminants with a protein adherent filter; (e) re-N-acetylating the purified capsular polysaccharide; and (f) ultrafiltration using a cellulose membrane having a cut-off of about 30 kDa again.